lbug 0.16.1

An in-process property graph database management system built for query speed and scalability
Documentation 
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#include "storage/compression/float_compression.h"

#include "alp/encode.hpp"
#include "common/system_config.h"
#include "common/utils.h"
#include <ranges>

namespace lbug {
namespace storage {

namespace {
static constexpr common::idx_t BITPACKING_CHILD_IDX = 0;

template<std::floating_point T>
common::LogicalType getBitpackingLogicalType() {
    if constexpr (std::is_same_v<T, float>) {
        return common::LogicalType::INT32();
    } else {
        return common::LogicalType::INT64();
    }
}
} // namespace

template<std::floating_point T>
size_t EncodeException<T>::numPagesFromExceptions(size_t exceptionCount) {
    return common::ceilDiv(static_cast<uint64_t>(exceptionCount),
        common::LBUG_PAGE_SIZE / sizeInBytes());
}

template<std::floating_point T>
size_t EncodeException<T>::exceptionBytesPerPage() {
    return common::LBUG_PAGE_SIZE / sizeInBytes() * sizeInBytes();
}

template<std::floating_point T>
bool EncodeException<T>::operator<(const EncodeException<T>& o) const {
    return posInChunk < o.posInChunk;
}

template<std::floating_point T>
EncodeException<T> EncodeExceptionView<T>::getValue(common::offset_t elementOffset) const {
    EncodeException<T> ret{};
    const auto* const elementAddress = bytes + elementOffset * decltype(ret)::sizeInBytes();
    std::memcpy(&ret.value, elementAddress, sizeof(ret.value));
    std::memcpy(&ret.posInChunk, elementAddress + sizeof(ret.value), sizeof(ret.posInChunk));
    return ret;
}

template<std::floating_point T>
void EncodeExceptionView<T>::setValue(EncodeException<T> exception,
    common::offset_t elementOffset) {
    auto* const elementAddress = bytes + elementOffset * decltype(exception)::sizeInBytes();
    std::memcpy(elementAddress, &exception.value, sizeof(exception.value));
    std::memcpy(elementAddress + sizeof(exception.value), &exception.posInChunk,
        sizeof(exception.posInChunk));
}

template<std::floating_point T>
FloatCompression<T>::FloatCompression()
    : constantEncodedFloatBitpacker(getBitpackingLogicalType<T>()), encodedFloatBitpacker() {}

template<std::floating_point T>
uint64_t FloatCompression<T>::compressNextPage(const uint8_t*&, uint64_t, uint8_t*, uint64_t,
    const struct CompressionMetadata&) const {
    UNREACHABLE_CODE;
}

template<std::floating_point T>
uint64_t FloatCompression<T>::compressNextPageWithExceptions(const uint8_t*& srcBuffer,
    uint64_t srcOffset, uint64_t numValuesRemaining, uint8_t* dstBuffer, uint64_t dstBufferSize,
    EncodeExceptionView<T> exceptionBuffer, [[maybe_unused]] uint64_t exceptionBufferSize,
    uint64_t& exceptionCount, const struct CompressionMetadata& metadata) const {
    DASSERT(metadata.compression == CompressionType::ALP);

    const size_t numValuesToCompress =
        std::min(numValuesRemaining, numValues(dstBufferSize, metadata));

    std::vector<EncodedType> integerEncodedValues(numValuesToCompress);
    for (size_t posInPage = 0; posInPage < numValuesToCompress; ++posInPage) {
        const auto floatValue = reinterpret_cast<const T*>(srcBuffer)[posInPage];
        const auto* floatMetadata = metadata.floatMetadata();
        const EncodedType encodedValue =
            alp::AlpEncode<T>::encode_value(floatValue, floatMetadata->fac, floatMetadata->exp);
        const double decodedValue =
            alp::AlpDecode<T>::decode_value(encodedValue, floatMetadata->fac, floatMetadata->exp);

        if (floatValue != decodedValue) {
            DASSERT(
                (exceptionCount + 1) * EncodeException<T>::sizeInBytes() <= exceptionBufferSize);
            exceptionBuffer.setValue(
                {.value = floatValue,
                    .posInChunk = common::safeIntegerConversion<uint32_t>(srcOffset + posInPage)},
                exceptionCount);

            // We don't need to replace with 1st successful encode as the integer bitpacking
            // metadata is already populated
            ++exceptionCount;
        } else {
            integerEncodedValues[posInPage] = encodedValue;
        }
    }
    srcBuffer += numValuesToCompress * sizeof(T);

    const auto* castedIntegerEncodedBuffer =
        reinterpret_cast<const uint8_t*>(integerEncodedValues.data());
    const auto compressedIntegerSize =
        getEncodedFloatBitpacker(metadata).compressNextPage(castedIntegerEncodedBuffer,
            numValuesToCompress, dstBuffer, dstBufferSize, metadata.getChild(BITPACKING_CHILD_IDX));

    // zero out unused parts of the page
    memset(dstBuffer + compressedIntegerSize, 0, dstBufferSize - compressedIntegerSize);

    // since we already do the zeroing we return the size of the whole page
    return dstBufferSize;
}

template<std::floating_point T>
uint64_t FloatCompression<T>::numValues(uint64_t dataSize, const CompressionMetadata& metadata) {
    return metadata.getChild(BITPACKING_CHILD_IDX)
        .numValues(dataSize, getBitpackingLogicalType<T>());
}

template<std::floating_point T>
void FloatCompression<T>::decompressFromPage(const uint8_t* srcBuffer, uint64_t srcOffset,
    uint8_t* dstBuffer, uint64_t dstOffset, uint64_t numValues,
    const struct CompressionMetadata& metadata) const {

    // use dstBuffer for unpacking the ALP encoded values then decode them in place
    getEncodedFloatBitpacker(metadata).decompressFromPage(srcBuffer, srcOffset, dstBuffer,
        dstOffset, numValues, metadata.getChild(BITPACKING_CHILD_IDX));

    static_assert(sizeof(EncodedType) == sizeof(T));
    auto* integerEncodedValues = reinterpret_cast<EncodedType*>(dstBuffer);
    for (size_t i = 0; i < numValues; ++i) {
        reinterpret_cast<T*>(dstBuffer)[dstOffset + i] =
            alp::AlpDecode<T>::decode_value(integerEncodedValues[dstOffset + i],
                metadata.floatMetadata()->fac, metadata.floatMetadata()->exp);
    }
}

template<std::floating_point T>
void FloatCompression<T>::setValuesFromUncompressed(const uint8_t* srcBuffer,
    common::offset_t srcOffset, uint8_t* dstBuffer, common::offset_t dstOffset,
    common::offset_t numValues, const CompressionMetadata& metadata,
    const common::NullMask* nullMask) const {
    // each individual value that is being updated should be able to be updated in place
    RUNTIME_CHECK(InPlaceUpdateLocalState localUpdateState{});
    DASSERT(numValues ==
            static_cast<common::offset_t>(
                std::ranges::count_if(std::ranges::iota_view{srcOffset, srcOffset + numValues},
                    [&localUpdateState, srcBuffer, &metadata, nullMask](common::offset_t i) {
                        auto value = reinterpret_cast<const T*>(srcBuffer)[i];
                        return (nullMask && nullMask->isNull(i)) ||
                               canUpdateInPlace(std::span(&value, 1), metadata, localUpdateState);
                    })));

    std::vector<EncodedType> integerEncodedValues(numValues);
    for (size_t i = 0; i < numValues; ++i) {
        const size_t posInSrc = i + srcOffset;

        const auto floatValue = reinterpret_cast<const T*>(srcBuffer)[posInSrc];
        const EncodedType encodedValue = alp::AlpEncode<T>::encode_value(floatValue,
            metadata.floatMetadata()->fac, metadata.floatMetadata()->exp);
        integerEncodedValues[i] = encodedValue;
    }

    getEncodedFloatBitpacker(metadata).setValuesFromUncompressed(
        reinterpret_cast<const uint8_t*>(integerEncodedValues.data()), 0, dstBuffer, dstOffset,
        numValues, metadata.getChild(BITPACKING_CHILD_IDX), nullMask);
}

template<std::floating_point T>
const CompressionAlg& FloatCompression<T>::getEncodedFloatBitpacker(
    const CompressionMetadata& metadata) const {
    if (metadata.getChild(BITPACKING_CHILD_IDX).isConstant()) {
        return constantEncodedFloatBitpacker;
    } else {
        return encodedFloatBitpacker;
    }
}

template<std::floating_point T>
BitpackInfo<typename FloatCompression<T>::EncodedType> FloatCompression<T>::getBitpackInfo(
    const CompressionMetadata& metadata) {
    const auto& bitpackMetadata = metadata.getChild(BITPACKING_CHILD_IDX);
    if (bitpackMetadata.isConstant()) {
        const auto constValue = bitpackMetadata.min.get<EncodedType>();
        return {.bitWidth = 0, .hasNegative = (constValue < 0), .offset = constValue};
    } else {
        return IntegerBitpacking<EncodedType>::getPackingInfo(bitpackMetadata);
    }
}

template<std::floating_point T>
bool FloatCompression<T>::canUpdateInPlace(std::span<const T> value,
    const CompressionMetadata& metadata, InPlaceUpdateLocalState& localUpdateState,
    const std::optional<common::NullMask>& nullMask, uint64_t nullMaskOffset) {
    size_t newExceptionCount = 0;
    std::vector<EncodedType> encodedValues(value.size());
    const auto bitpackingInfo = getBitpackInfo(metadata);
    const auto* floatMetadata = metadata.floatMetadata();
    for (size_t i = 0; i < value.size(); ++i) {
        if (nullMask && nullMask->isNull(nullMaskOffset + i)) {
            continue;
        }

        const auto floatValue = value[i];
        const EncodedType encodedValue =
            alp::AlpEncode<T>::encode_value(floatValue, floatMetadata->fac, floatMetadata->exp);
        const double decodedValue =
            alp::AlpDecode<T>::decode_value(encodedValue, floatMetadata->fac, floatMetadata->exp);
        if (floatValue != decodedValue) {
            ++newExceptionCount;
            encodedValues[i] = bitpackingInfo.offset;
        } else {
            encodedValues[i] = encodedValue;
        }
    }
    localUpdateState.floatState.newExceptionCount += newExceptionCount;
    const size_t totalExceptionCount =
        floatMetadata->exceptionCount + localUpdateState.floatState.newExceptionCount;
    const bool exceptionsOK = totalExceptionCount <= floatMetadata->exceptionCapacity;

    return exceptionsOK &&
           metadata.getChild(BITPACKING_CHILD_IDX)
               .canUpdateInPlace(reinterpret_cast<uint8_t*>(encodedValues.data()), 0,
                   encodedValues.size(), getBitpackingLogicalType<T>().getPhysicalType(),
                   localUpdateState);
}

template<std::floating_point T>
common::page_idx_t FloatCompression<T>::getNumDataPages(common::page_idx_t numTotalPages,
    const CompressionMetadata& compMeta) {
    return numTotalPages -
           EncodeException<T>::numPagesFromExceptions(compMeta.floatMetadata()->exceptionCapacity);
}

template class FloatCompression<double>;
template class FloatCompression<float>;

template struct EncodeException<double>;
template struct EncodeException<float>;

template struct EncodeExceptionView<double>;
template struct EncodeExceptionView<float>;

} // namespace storage
} // namespace lbug